Preheat oven to 160°C / 340°F. Line a 20cm springform pan with parchment paper.
Separate egg whites and yolks into two bowls.
Whisk yolks with condensed milk, lemon juice, zest, and yogurt.
Beat egg whites until stiff peaks form.
Fold egg whites gently into yolk mixture.
Pour into pan. Place pan in larger water-filled pan.
Bake 45 minutes. Let cool in oven.
Chill for 2–3 hours. Dust with sugar if desired. Slice and serve.
